In Norway, about 30 subsea tunnels have been constructed over the last 20 years. The minimum depth of 17 subsea tunnels is 56 m and rock cover are between 23 and 49 m. As the project areas for subsea tunnel are covered by water, special investigation techniques need to be applied and the investigation results are more uncertain than that of most conventional tunnel projects. The indefinite potential of water inflow and the salinic character of ingress water represent considerable problems for tunnel equipment and rock support materials. The least stable conditions are represented by major faults or weakness zones containing heavily crushed rock and clay gouge. This paper introduces the Oslofjord subsea tunnel project including minimum rock cover requirement, risk of water inflow, investigation costs, construction costs, and traffic & operation costs.

The influence of round length on the tunnel stability and construction cost is well acknowledged by many researchers and engineers but the coherent procedure is not available for its determination. In this study, the behaviour modes of the face and unsupported span was investigated for weak rock tunnel by a small scale model test, PFC3D and FDM analyses in consideration of the round length. Total five types of behaviour modes are defined and quantitative estimation of the behaviour modes was established in terms of the safety factor for the face stability and the conditional chart. Although the proposed method has some restrictions, this method can provide useful information for the optimization of the round length and excavation, especially in design stage.

Research and development for disposal of contaminants including radioactive wastes in deep underground have been carried out from laboratory works. However, validation and reliability of the data from the laboratory are arguing issues because they are not obtained from real disposal situations. Underground research laboratory (URL) is not only a solution to overcome such limitations, but also a valuable facility for performance assessment as an engineering scale. However, it requires much budget, and environmental issues can give rise to social conflicts easily. Such considering points related to URL are discussed as well as current status of worldwide URLs are introduced. Furthermore study plans for solute transport in a small-scale underground research tunnel (KURT), which was authorized recently as an non-radioactive facility in Korea, also described.

The 11 nuclear power plants have been taking charge of more than 40% of the total electrical power development in Korea. In addition to the existing nuclear power plants at Gori, Wolsung, Youngkwang, etc., the 12 nuclear power plants are expected to be newly established until 2006. So, the 23 nuclear power plants will produce the electric power as much as more than 50% of the national gross production. However the nuclear power plants are inevitably generating the detrimental atomic wastes. Therefore the disposal techniques for the nuclear wastes should be ensured considering a very high safety factor. According to the basic researches in KAERI, the underground disposal repositories are reported to be most favorable for Korea. The KBS-3 disposal system has been strongly suggested by KAERI and this system has a deep tunnel with several disposal boreholes in tunnel floor. The nuclear wastes, which are sealed tightly in a canister, will be disposed in these boreholes. Considering the disposal tunnel in a great depth, the in-situ stress regimes will affect severely the tunnel stability. Consequently the effect of the in-situ stresses on the disposal tunnel and the role of the in-situ stresses in tunnel stability analysis are examined by the numerical studies.

Severe damage can occur around deposition holes due to complex interaction of thermo-hydro-mechanical (THM) loading during the long term operation of high level radioactive waste repository. Many candidate sites for repository are located in crystalline rock mass, therefore mechanism of damage follows the form of brittle fracture and failure. This paper briefly introduces major outcomes from 15 years international collaborative project, DECOVALEX, and presents major study results for current ongoing benchmark test study from DECOVALEX-THMC, to evaluate the effect of THM loading to rock mass in excavation damaged zone (EDZ) near deposition holes. Through benchmark test model by simplifying THM loading to boundary loading obtained numerical results are compared, and discrete fracture interaction after up to 1 million years operation is discussed.

An underground research tunnel, KURT, was constructed at Korea Atomic Energy Research Institute, for various in situ validation experiments related to the development of a high-level radioactive waste disposal system. KURT, which has length of 255 m (access tunnel 180 m and research modules 75 m) and size of was excavated in a cryatalline rock mass. In the KURT project, different rock mechanics studies had been carried out during the concept design, site characterization, detailed design, and construction stages. From the geophysical survey, borehole investigation, and rock property tests in laboratory and in situ, the rock and rock mass properties required for the mechanicsl stability analysis of KURT could be achieved and used for the input parameters of computer simulations. In this paper, important results from the rock mechanics studies at KURT and the three-dimensional mechanical stability analysis will be introduced.

A new underground LNG storage concept in the rock mass has been developed by combining underground cavern construction and new ice-ring harrier technologies with the conventional cryogenic insulation system. Technical feasibility of the storage system has been verified through construction and operation of the pilot storage cavern and a full-scale project is expected to start in the near future. One of the most important issues in the LNG storage system is the operational efficiency of the storage to minimize heat loss during a long period of operation due to the cryogenic heat transfer. This paper presents several important results of heat transfer and coupled hydro-thermal analyses by a finite element code Temp/W and Seep/W. A series of heat transfer analyses for full-scale caverns were performed to determine design parameters such as boil-off gas ratio (BOR), insulation thickness and pillar width. The result of the coupled hydro-mechanical analysis showed that BOR for underground storage system remains at about 0.04 %/day during the early stage of the operation. This value could be even much lower when the discontinuities in the rock masses are taken into consideration.

The analysis of ground subsidence stability was conducted for the residential area located on the limestone corrosion zone. For the investigation of the cavity distribution in limestone region, various geophysical investigations such as electroresistivity tomography, electromagnetic prospecting are carried out. Geotechnical field tests with drilling are also carried out for the evaluation of the ground characteristics. Based upon their results, numerical modeling is performed for the simulation and prediction of the ground subsidence with the conditions of cavity geometry and groundwater level. The main factor to cause the ground subsidence is estimated as the draw down of the groundwater level below soil overburden, which disturbs the mechanical equilibrium of ground and drives washing away the overburden soil through the cavity and solace subsidence. It seemed that it is essential to maintain the groundwater level continuously above the shallow cavity for the prevention of the ground subsidence on the limestone corrosion zone.